Search Results (18)

Intracortical microstimulation (ICMS) is a promising approach for visual prostheses. We recently proposed using retinal neuromorphic spike trains derived from visual images as ICMS pulse sequences, and preliminarily recorded cortical voltage-sensitive dye (VSD) responses to such stimulation. To examine whether these cortical responses contain image information, we explore the feasibility of machine-learning–based decoding. However, constructing such a decoder requires large-scale datasets linking visual images, spike trains, and cortical responses, which are not yet experimentally available. Therefore, we generated surrogate data with a Wiener-system model that simulates VSD responses of the visual cortex to ICMS pulse trains. A convolutional neural network trained on these synthetic datasets successfully reconstructed images from the simulated cortical responses. This simulation work serves as a proof-of-concept study, demonstrating the computational feasibility of estimating visual information contained in neuromorphic ICMS-evoked cortical activity and providing a foundation for future physiological validation. Full article

This review addresses the challenges of obtaining high-quality quantitative data in the optical imaging of membrane voltage and calcium dynamics. The paper provides a comprehensive overview and systematization of recent studies that analyze factors limiting signal fidelity and propose strategies to enhance data quality. The primary sources of signal degradation in biological optical imaging, with an emphasis on membrane voltage and calcium imaging, are systematically explored across four major indicator classes: voltage-sensitive dyes (VSDs), genetically encoded voltage indicators (GEVIs), calcium-sensitive dyes (CSDs), and genetically encoded calcium indicators (GECIs). Common mechanisms that compromise data quality are classified into three main categories: fundamental photon shot noise, device-related errors, and sample-related measurement errors. For each class of limitation, its physical or biological origin and characteristic manifestations are described, which are followed by an analysis of available mitigation strategies, including hardware optimization, choice of sensors, sample preparation and experimental design, post-processing and computational correction methods. Full article

Advancements in cellular imaging have significantly enhanced our understanding of membrane potential and Ca²⁺ dynamics, which are crucial for various cellular processes. Voltage-sensitive dyes (VSDs) are pivotal in this field, enabling non-invasive, high-resolution visualization of electrical activity in cells. This review discusses the various types of VSDs, including electrochromic, Förster Resonance Energy Transfer (FRET)-based, and Photoinduced Electron Transfer (PeT)-based dyes. VSDs are essential tools for studying mitochondrial activity and neuronal function and are frequently used in conjunction with Ca²⁺ indicators to elucidate the complex relationship between membrane potential and Ca²⁺ fluxes. The development of novel dyes with improved photostability and reduced toxicity continues to expand the potential of VSDs in biomedical research. This review underscores the importance of VSDs in advancing our understanding of cellular bioenergetics, signaling, and disease mechanisms. Full article

Optical mapping is a powerful imaging technique widely adopted to measure membrane potential changes and intracellular Ca²⁺ variations in excitable tissues using voltage-sensitive dyes and Ca²⁺ indicators, respectively. This powerful tool has rapidly become indispensable in the field of cardiac electrophysiology for studying depolarization wave propagation, estimating the conduction velocity of electrical impulses, and measuring Ca²⁺ dynamics in cardiac cells and tissues. In addition, mapping these electrophysiological parameters is important for understanding cardiac arrhythmia mechanisms. In this review, we delve into the fundamentals of cardiac optical mapping technology and its applications when applied to hiPSC-derived cardiomyocytes and discuss related advantages and challenges. We also provide a detailed description of the processing and analysis of optical mapping data, which is a crucial step in the study of cardiac diseases and arrhythmia mechanisms for extracting and comparing relevant electrophysiological parameters. Full article

The optical imaging of neuronal activity with potentiometric probes has been credited with being able to address key questions in neuroscience via the simultaneous recording of many neurons. This technique, which was pioneered 50 years ago, has allowed researchers to study the dynamics of neural activity, from tiny subthreshold synaptic events in the axon and dendrites at the subcellular level to the fluctuation of field potentials and how they spread across large areas of the brain. Initially, synthetic voltage-sensitive dyes (VSDs) were applied directly to brain tissue via staining, but recent advances in transgenic methods now allow the expression of genetically encoded voltage indicators (GEVIs), specifically in selected neuron types. However, voltage imaging is technically difficult and limited by several methodological constraints that determine its applicability in a given type of experiment. The prevalence of this method is far from being comparable to patch clamp voltage recording or similar routine methods in neuroscience research. There are more than twice as many studies on VSDs as there are on GEVIs. As can be seen from the majority of the papers, most of them are either methodological ones or reviews. However, potentiometric imaging is able to address key questions in neuroscience by recording most or many neurons simultaneously, thus providing unique information that cannot be obtained via other methods. Different types of optical voltage indicators have their advantages and limitations, which we focus on in detail. Here, we summarize the experience of the scientific community in the application of voltage imaging and try to evaluate the contribution of this method to neuroscience research. Full article

Plant extracts have been utilized as an ecofriendly natural reducing agent for the synthesis of nanomaterials, including metal oxides. Prickly pear (opuntia) fruit extract (PPE) was used as a reducing agent for the sol–gel synthesis of titanium dioxide nanoparticles (TiO₂ NPs) and as a sensitizer for the TiO₂ NPs photoanode used in dye-sensitized solar cells (DSSCs). Ultraviolet-visible and infrared spectra, X-ray diffraction patterns, and scanning electron microscopic images were confirmed in the formation of semiconducting TiO₂ NPs with the predominate size of ~300 nm. The use of PPE rendered discrete TiO₂ NPs, whereas the typical synthesis without PPE resulted TiO₂ aggregates. TiO₂ NPs had a tetragonal crystalline structure, and their grain size was varied with respect to the concentration of PPE. The size of TiO₂ crystallites was found to be 20, 19, 15, and 10 nm when the volume percentage of PPE was 0.2, 0.4, 0.6, and 0.8%, respectively. TiO₂ NPs obtained using PPE were coated on indium-doped tin oxide substrates and sensitized with natural dye made up of PPE and synthetic dyes, namely rose Bengal (RB) and eosin yellow (EY). The photoanode fabricated with dye-sensitized TiO₂ NPs was subjected to current–voltage response studies. The maximum power-conversion efficiency, 1.4%, was recorded for photoanodes sensitized with PPE dye, which is considerably higher than that for RB (1.16%) or EY (0.8%). Overall, the above findings proved that PPE can be used as a potential reducing/capping agent and TiO₂ sensitizer for DSSC applications. Full article

Membrane potential is a fundamental property of biological cells. Changes in membrane potential characterize a vast number of vital biological processes, such as the activity of neurons and cardiomyocytes, tumorogenesis, cell-cycle progression, etc. A common strategy to record membrane potential changes that occur in the process of interest is to utilize organic dyes or genetically-encoded voltage indicators with voltage-dependent fluorescence. Sensors are introduced into target cells, and alterations of fluorescence intensity are recorded with optical methods. Techniques that allow recording relative changes of membrane potential and do not take into account fluorescence alterations due to factors other than membrane voltage are already widely used in modern biological and biomedical studies. Such techniques have been reviewed previously in many works. However, in order to investigate a number of processes, especially long-term processes, the measured signal must be corrected to exclude the contribution from voltage-independent factors or even absolute values of cell membrane potential have to be evaluated. Techniques that enable such measurements are the subject of this review. Full article

The substantia nigra is generally considered to show significant cell loss not only in Parkinson’s but also in Alzheimer’s disease, conditions that share several neuropathological traits. An interesting feature of this nucleus is that the pars compacta dopaminergic neurons contain acetylcholinesterase (AChE). Independent of its enzymatic role, this protein is released from pars reticulata dendrites, with effects that have been observed in vitro, ex vivo and in vivo. The part of the molecule responsible for these actions has been identified as a 14-mer peptide, T14, cleaved from the AChE C-terminus and acting at an allosteric site on alpha-7 nicotinic receptors, with consequences implicated in neurodegeneration. Here, we show that free T14 is co-localized with tyrosine hydroxylase in rodent pars compacta neurons. In brains with Alzheimer’s pathology, the T14 immunoreactivity in these neurons increases in density as their number decreases with the progression of the disease. To explore the functional implications of raised T14 levels in the substantia nigra, the effect of exogenous peptide on electrically evoked neuronal activation was tested in rat brain slices using optical imaging with a voltage-sensitive dye (Di-4-ANEPPS). A significant reduction in the activation response was observed; this was blocked by the cyclized variant of T14, NBP14. In contrast, no such effect of the peptide was seen in the striatum, a region lacking the T14 target, alpha-7 receptors. These findings add to the accumulating evidence that T14 is a key signaling molecule in neurodegenerative disorders and that its antagonist NBP14 has therapeutic potential. Full article

The dye-sensitized solar cells microfluidically integrated with a redox flow battery (µDSSC-RFB) belong to a new emerging class of green energy sources with an inherent opportunity for energy storage. The successful engineering of microfluidically linked systems is, however, a challenging subject, as the hydrodynamics of electrolyte flow influences the electron and species transport in the system in several ways. In the article, we have analyzed the microflows hydrodynamics by means of the lattice-Boltzmann method, using the algebraic solution of the Navier-Stokes equation for a duct flow and experimentally by the micro particle image velocimetry method. Several prototypes of µDSSC were prepared and tested under different flow conditions. The efficiency of serpentine µDSSC raised from 2.8% for stationary conditions to 3.1% for electrolyte flow above 20 mL/h, while the fill factor increased about 13% and open-circuit voltage from an initial 0.715 V to 0.745 V. Although the hexagonal or circular configurations are the straightforward extensions of standard photo chambers of solar cells, those configurations are hydrodynamically less predictable and unfavorable due to large velocity gradients. The serpentine channel configuration with silver fingers would allow for the scaling of the µDSSC-RFB systems to the industrial scale without loss of performance. Furthermore, the deterioration of cell performance over time can be inhibited by the periodic sensitizer regeneration, which is the inherent advantage of µDSSC. Full article

Studies using functional magnetic resonance imaging assume that hemodynamic responses have roughly linear relationships with underlying neural activity. However, to accurately investigate the neurovascular transfer function and compare its variability across brain regions, it is necessary to obtain full-field imaging of both electrophysiological and hemodynamic responses under various stimulus conditions with superior spatiotemporal resolution. Optical imaging combined with voltage-sensitive dye (VSD) and intrinsic signals (IS) is a powerful tool to address this issue. We performed VSD and IS imaging in the primary (S1) and secondary (S2) somatosensory cortices of rats to obtain optical maps of whisker-evoked responses. There were characteristic differences in sensory responses between the S1 and S2 cortices: VSD imaging revealed more localized excitatory and stronger inhibitory neural activity in S1 than in S2. IS imaging revealed stronger metabolic responses in S1 than in S2. We calculated the degree of response to compare the sensory responses between cortical regions and found that the ratio of the degree of response of S2 to S1 was similar, irrespective of whether the ratio was determined by VSD or IS imaging. These results suggest that neurovascular coupling does not vary between the S1 and S2 cortices. Full article

We evaluated the mechanisms underlying the spinal cord stimulation (SCS)-induced analgesic effect on neuropathic pain following spared nerve injury (SNI). On day 3 after SNI, SCS was performed for 6 h by using electrodes paraspinally placed on the L4-S1 spinal cord. The effects of SCS and intraperitoneal minocycline administration on plantar mechanical sensitivity, microglial activation, and neuronal excitability in the L4 dorsal horn were assessed on day 3 after SNI. The somatosensory cortical responses to electrical stimulation of the hind paw on day 3 following SNI were examined by using in vivo optical imaging with a voltage-sensitive dye. On day 3 after SNI, plantar mechanical hypersensitivity and enhanced microglial activation were suppressed by minocycline or SCS, and L4 dorsal horn nociceptive neuronal hyperexcitability was suppressed by SCS. In vivo optical imaging also revealed that electrical stimulation of the hind paw-activated areas in the somatosensory cortex was decreased by SCS. The present findings suggest that SCS could suppress plantar SNI-induced neuropathic pain via inhibition of microglial activation in the L4 dorsal horn, which is involved in spinal neuronal hyperexcitability. SCS is likely to be a potential alternative and complementary medicine therapy to alleviate neuropathic pain following nerve injury. Full article

During visual fixation, the eyes make small and fast movements known as microsaccades (MSs). The effects of MSs on neural activity in the visual cortex are not well understood. Utilizing voltage-sensitive dye imaging, we imaged the spatiotemporal patterns of neuronal responses induced by MSs in early visual cortices of behaving monkeys. Our results reveal a continuous “visual instability” during fixation: while the visual stimulus moves over the retina with each MS, the neuronal activity in V1 ‘hops’ within the retinotopic map, as dictated by the MS parameters. Neuronal modulations induced by MSs are characterized by neural suppression followed by neural enhancement and increased synchronization. The suppressed activity may underlie the suppressed perception during MSs whereas the late enhancement may facilitate the processing of new incoming image information. Moreover, the instability induced by MSs applies also to neural correlates of visual perception processes such as figure-ground (FG) segregation, which appear to develop faster after fixational saccades. Full article

Incorporating optical methods into implantable neural sensing devices is a challenging approach for brain–machine interfacing. Specifically, voltage-sensitive dye (VSD) imaging is a powerful tool enabling visualization of the network activity of thousands of neurons at high spatiotemporal resolution. However, VSD imaging usually requires removal of the dura mater for dye staining, and thereafter the exposed cortex needs to be protected using an optically transparent artificial dura. This is a major disadvantage that limits repeated VSD imaging over the long term. To address this issue, we propose to use an atelocollagen membrane as the dura substitute. We fabricated a small cranial chamber device, which is a tubular structure equipped with a collagen membrane at one end of the tube. We implanted the device into rats and monitored neural activity in the frontal cortex 1 week following surgery. The results indicate that the collagen membrane was chemically transparent, allowing VSD staining across the membrane material. The membrane was also optically transparent enough to pass light; forelimb-evoked neural activity was successfully visualized through the artificial dura. Because of its ideal chemical and optical manipulation capability, this collagen membrane may be widely applicable in various implantable neural sensors. Full article

Optogenetics is an emerging method that uses light to manipulate electrical activity in excitable cells exploiting the interaction between light and light-sensitive depolarizing ion channels, such as channelrhodopsin-2 (ChR2). Initially used in the neuroscience, it has been adopted in cardiac research where the expression of ChR2 in cardiac preparations allows optical pacing, resynchronization and defibrillation. Recently, optogenetics has been leveraged to manipulate cardiac electrical activity in the intact heart in real-time. This new approach was applied to simulate a re-entrant circuit across the ventricle. In this technical note, we describe the development and the implementation of a new software package for real-time optogenetic intervention. The package consists of a single LabVIEW program that simultaneously captures images at very high frame rates and delivers precisely timed optogenetic stimuli based on the content of the images. The software implementation guarantees closed-loop optical manipulation at high temporal resolution by processing the raw data in workstation memory. We demonstrate that this strategy allows the simulation of a ventricular tachycardia with high stability and with a negligible loss of data with a temporal resolution of up to 1 ms. Full article

Pacemaker cardiomyocytes of the sinoatrial node (SAN) beat more rapidly than cells of the working myocardium. Beating in SAN cells responds to β-adrenergic and cholinergic signaling by speeding up or slowing, respectively. Beat rate has traditionally been assessed using voltage or calcium sensitive dyes, however these may not reflect the true rate of beating because they sequester calcium. Finally, in vitro differentiated cardiomyocytes sometimes briefly pause during imaging giving inaccurate beat rates. We have developed a MATLAB automation to calculate cardiac beat rates directly from video clips based on changes in pixel density at the edges of beating areas. These data are normalized to minimize the effects of secondary movement and are converted to frequency data using a fast Fourier transform (FFT). We find that this gives accurate beat rates even when there are brief pauses in beating. This technique can be used to rapidly assess beating of cardiomyocytes in organoid culture. This technique could also be combined with field scanning techniques to automatically and accurately assess beating within a complex cardiac organoid. Full article